The oculocerebrorenal syndrome of Lowe (LOCRS) is an X-linked inborn error of metabolism of unknown etiology. Affected males are retarded and have congenital cataracts and renal tubular dysfunction. Carrier females frequently show lens opacities that may aid in heterozygote detection but are not fully sensitive or specific. Prenatal diagnosis is not possible. The locus for LOCRS has been mapped to the Xq25 region by linkage to restriction fragment length polymorphisms (RFLPs) in Xq24-26 and by the occurrence of LOCRS in a female with an X/3 translocation with breakpoint at Xq25. The project will be carried out in two phases: Phase 1: We propose to use the X;3 translocation cell line to generate somatic cell hybrids in which the der X and der 3 are isolated away from the normal X. These hybrids will allow us to map a set of independent cosmid clones from the Xq24-26 region with respect to the Xq25 breakpoint. Cosmids that flank the breakpoint will be used to search for a number of RFLPs in order to generate highly informative flanking markers for LOCRS. These RFLPS will be tested for linkage to LOCRS in a set of 6 families segregating for the disease. If recombination is seen with a particular flanking cosmid, additional cosmids will be analyzed for RFLPs until a pair of tightly linked flanking markers is identified. Phase 2: The molecular distance between the LOCRS locus and the Xq24-26 cosmid sequences will be estimated in two different ways. First, large restriction fragments from the X;3 translocation line and the hybrids containing derX or der3 will be separated by pulsed-field gel electrophoresis and probed with Xq24-26 cosmid sequences to look for an aberrant fragment cuased by the breakpoint. A cosmid within 500 kb of the breakpoint is likely to be found among the set of greater than 50 cosmid clones that will be available. Second, a panel of DNA from 41 independent patients with LOCRS will be screened with these same Xq24-26 cosmids to look for an interstitial deletion affecting the LOCRS. Identification of a cosmid sequence within a measurable molecular distance of the LOCRS locus is an important first step towards gene isolation.